1. Field of the Invention
This invention relates to mechanisms for indicating the status of the locking mechanism of a conventional locking door latch mechanism and more particularly, to a replacement interior doorknob having a self contained battery energized audio and/or visual indicating means sensing whether the locking mechanism which prevents the exterior knob from turning is disengaged.
2. Description of the Prior Art
Alarm systems for indicating the locked or unlocked status of a door or other movable partition closing an entryway are common and well known. Such alarm systems can be divided into several common categories.
The mechanisms in the most common category typically include a mechanism which electrically or otherwise senses the position of a bolt securing the door or other partition across the entryway. For example, U.S. Pat. No. 4,178,587, F. W. Jamison, describes a system for sensing the engaged position of a bolt involving a small "normally-closed" (micro)switch which is held in an open position by the bold in its engaged or locked position. Dislodging or disengaging the bolt allows the "normally-closed" switch to close, completing an electrical circuit which includes a source of electrical energy and an electrically energized indicating means such as a buzzer or light. Various different types of switching mechanisms for sensing the presence or absence of a bolt securing a door or partition across an entry way are described in U.S. Pat. No. 4,465,997, T. N. Hines.
Another common category of alarm systems senses whether or not the door or partition closing the entryway is ajar. Probably the most common type of alarm system in this latter category includes a magnetically energized "normally-open" reed switch located on the stationary door frame and held closed by a magnet mounted on the moving door or partition when the door is closed. When the door or partitioned is moved, moving the magnet away from the reed switch, the reed switch opens, thereby interrupting an electrical circuit and triggering an alarm circuit which typically includes a source of electrical energy and an electrically energized audio and/or visual alarm indicator. Alarm systems of this latter category are typically utilized for the purpose of detecting unauthorized entry. A variation of the above system is described in U.S. Pat. No. 4,516,114, R. C. Cook.
Other categories of lock monitoring alarm systems include optical sensors and magnetic switches, as well as small electrical microswitches for sensing a combination of different parameters relative to a locked door or partition closing a entryway. For example, U.S. Pat. No. 4,453,390, P. G. Moritz, et al, describes a combination lock monitoring system which involves the use of photosensitive means responding to light reflecting off of particular areas of both a lock bolt mechanism and a lock drop arm, in combination with one or more "normally-open" microswitches closing responsive to closure of a partition and engagement of a time lock mechanism.
Summarizing, while there are many different types of monitoring systems for providing an alarm indicating that a door or partition is unlocked, such systems typically require components mounted in both the frame of the entryway and the door. Additionally, existing lock monitoring alarm systems require an electrical connection between a switching mechanism and an external electrical energizing and alarm circuit. Consequently, such systems are typically mounted in the frame of the portal rather than in the moving door or partition.
The primary disadvantage of existing lock monitoring alarm systems is the necessity for electrical wiring coupling a switching mechanism into an alarm circuit. This limitation has discouraged use of such systems by the general public except in those instances where the risk of loss economically justifies installation of such a system. For example, with existing systems it has not been considered feasible to retrofit each door of a hotel equipped with common lockable door latching mechanisms with lock monitoring alarm systems.
Furthermore, such lock monitoring alarm systems have not been considered economically feasible for doorways between rooms in a common structure wherein a manually actuated locking mechanisms are incorporated into the interior knob for engaging and releasing a locking mechanism preventing the exterior knob from turning, e.g. a bathroom door.
Finally, externally wired lock monitoring systems have simply not been accepted by the general public for use in their residual dwellings. The doorways of such dwellings typically include one or more lockable door latching mechanisms with turnable exterior and interior knobs engaging a spindle moving the door bolt. Typically, such residential door latching mechanisms include an exterior key activated mechanism, often incorporated into the exterior knob for operating a locking mechanism located within the frame of the door preventing rotation of the exterior knob, and an interior manually operable mechanism for engaging and releasing the locking mechanism.